The invention relates to an antenna system with a plurality of individual antennae in each case connected in a separate drive path, to which a common signal transmitter is assigned, and with a triggering unit provided for selective connecting a drive path selected in each case. It also relates to an access control system for a vehicle with such an antenna system as well as a method for detecting a defective individual antenna in such an antenna system.
Vehicles can be fitted with so-called “Keyless Entry” systems for raising user comfort and also for increasing theft security, in which keyless opening and closing of the central locking and if required also additional releasing of the engine immobiliser can occur by means of a transponder or a mobile identification transmitter. In such systems a control system of the vehicle communicates via coded signals with the respective identification transmitter, whereby for example on receipt of corresponding signals from the information transmitter and their evaluation in case of positive identification of an authorised user corresponding releasing of the central locking and/or for releasing the engine immobiliser or the like can be issued.
For communication with the identification transmitter or transponder the control system transmits appropriate signals to the latter. Signal transmission occurs at the same time usually via a suitable antenna system integrated into the vehicle. Due to the large number of possible applications and individual cases to be considered is provided usually a multichannel antenna system at the same time, in which a plurality of satisfactorily designed individual antennae, if required also arranged in the vehicle, in each case connected in a separate drive path, is used. The individual antennae can on the one hand for example be so-called internal and on the other hand so-called external antennae, whereby their range and the like can be specifically detected via an internal antenna based on its arrangement in the vehicle as to whether the respective identification transmitter or transponder is currently in the vehicle interior itself. In the case however of an external antenna the individual antenna provided therefor with respect to dimensioning and positioning for communication with the identification transmitter or trans-ponder is configured for the case where the latter is located on the exterior of the vehicle. To be able to consider another dependence on direction or the like at the same time if required, a plurality of such specialised antennae can be provided in the antenna system in addition both in the Interior region and also in the exterior region.
An antenna system of this type, in which the individual antennae are assigned a common signal transmitter for required communication with the identification transmitter or transponder, whereby selective activation or connecting a desired situation-dependent individual antenna by selecting its respective drive path via a central triggering unit is provided, is known for example from DE 10 2004 058 613 A1. This system receives reliable supply of transmission signals to the antennae in particular using comparatively simple means, whereby unwanted coupling or crosstalk effects can be reliably prevented.
However, as it has eventuated, basically with antenna systems of the above-mentioned multichannel structure in the event of error, therefore when one or more of the individual antennae drop out, error search is comparatively complicated, therefore identification of the defective antenna in particular. In particular, repair expenses in the event of breakdown can be undesirably high.
The object of the invention therefore is to further develop an antenna system of the abovementioned type, such that particularly simply reliable identification of a defective individual antenna is enabled in the event of error. A particularly favourable method for detecting a defective individual antenna in such an antenna system will also be specified.